The invention relates to a four-stroke internal-combustion engine for driving a motor vehicle having inlet and outlet charge exchange valves and with an additional outlet valve, adjustable by means of an actuating device and intended for each cylinder; and with a throttle flap arranged in the outlet channel of the internal-combustion engine, adjustable by means of an actuating mechanism. The actuating devices and mechanism are actuable by at least one directional valve adjustable in dependence on a brake switch. At speeds above a predetermined limiting speed, a braking of the internal-combustion engine occurs as a result of the opening of the additional outlet valves and by a throttling of the exhaust gases.
German Offenlegungsschrift 3,428,626 makes known a four-stroke internal-combustion engine, in which braking is brought about by virtue of the fact that during the entire braking operation, compressed air is conveyed out of the cylinder space into the outlet channel of the internal-combustion engine via additional outlet valves actuated by an adjusting device and wherein the exhaust gases of the internal-combustion engine are throttled by a throttle flap adjustable by means of an actuating device, located in the outlet channel of the internal-combustion engine. The adjusting device and the actuating device are controlled by a directional valve operable in dependence on the brake pedal. As a result of the actuation of the brake pedal, depending on the directional valve, the actuation of the additional outlet valves and of the exhaust-gas throttle flap can take place in any sequence and combination.
When the additional outlet valves are open, engine ignition is no longer possible. The result of this is that the engine can die, if at the same time, it is running in the idling range.
The object of the invention is to design an internal-combustion engine of the above general type, so that reliable engine running is guaranteed over the entire speed range and without detriment to the braking of the vehicle.
According to the invention, the object is achieved by virtue of the fact that the engine braking is cancelled below a specific speed limit.
For this purpose, in the control circuit of the engine brake there is a speed switch which prevents either the opening of the additional outlet valves and/or additionally the closing of the exhaust-gas throttle flap when the speed of the internal-combustion engine falls below a lower limiting value. In the idling range of the internal-combustion engine, the effect of the engine brake is thus at least partially cancelled and the engine is reliably prevented from dying.
The additional exhaust valves can discharge directly into the exhaust channel or directly into the ambient air and by-passing the exhaust channel.
It is advantageous if the actuating controls are controlled by a pressure medium (air or oil) in response to movement of an operated control valve. Separate control of the throttle and additional exhaust valves can be obtained by utilizing two control valves.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.